Cadmium (Cd) is an environmental pollutant which is toxic to a number of tissues. The long-term goal of our research is to better understand the mechanisms of toxicity and how metallothionein can alter its toxicity, so that we can both protect and treat humans from Cd toxicity. The metal is highly cumulative with a biological half-life of 10-40 years in humans. Over half of the total body burden is concentrated in liver and kidney, and of this, most is bound to metallothionein (MT). The present proposal has three specific aims. The first (1) is to examine the function of MT. Establishing the functions of MT remain elusive because there has been no experimental method of increasing MT without producing other effects. For example, metals, such as zinc, have been used to induce MT, but in addition to increasing MT, these metals also produce a myriad of other biological effects. Thus, it has been difficult to ascertain a direct cause and effect role for MT. The investigators recently have obtained transgenic mice that normally possess MT levels about 40-times higher than their non-transgenic counterparts. These animals provide a unique model for studying the protective role of MT without the introduction of agents that also alter other important systems. They plan to use these mice to determine MT's role in protecting against Cd-induced hepatotoxicity, cisplatin-induced nephrotoxicity, and oxidative stress produced by adriamycin, paraquat, and X-rays. In the (2) second aim, they plan to investigate the cellular regulation of MT in rat and human liver cells. They have shown that basal levels of MT are extremely important in determining the susceptibility of cells to the toxic effects of Cd. Human liver has about 50-100 times more MT than rat liver. They plan to determine the biochemical and molecular reasons for the differences between human and rats. That is, whether there is a difference in degradation and/or synthesis of MT, and if there is an increased synthesis, are the mRNA levels higher. If mRNA levels are higher, they will determine if this is due to increased synthesis and/or slower degradation of MT mRNA in humans than in rats. They will also test the hypothesis that the high basal level of MT gene expression in humans is due to species-specific trans-acting factor(s) not present in rats. In the (3) third aim, they plan to use renal proximal tubule cell culture systems to investigate the mechanism of CdMT nephrotoxicity, the main target organ of Cd toxicity in humans. From the proposed experiments using transgenic animals they will determine with certainty the functions of MT in protecting us from toxicants, using molecular biology techniques they will determine the mechanism by which humans have much more MT than rats, and using tissue culture techniques, determine the mechanisms of CdMT-induced nephrotoxicity.